This invention pertains to an efficient, high recovery, single product process for converting low BTU gas to high BTU methane gas using a unique combination of known processes. More particularly, high purity methane is produced by standard methanation of a balanced carbon monoxide-hydrogen feed gas derived from a unique combination of steps involving separating carbon monoxide first and then generating hydrogen in two separate ways, that is, by hydride formation and decomposition and by water-gas shift reaction of some of the carbon monoxide.
This disclosure relates to a process for producing methane from a gas containing hydrogen, carbon monoxide, nitrogen and the other components normally found in the gas produced by the gasification of carbonaceous materials with air. This gaseous product is sometimes called producer gas. By way of example, a producer gas produced from the gasification of coal may contain on a dry basis 15% hydrogen, 29% carbon monoxide, 50% nitrogen, 5% carbon dioxide and 1% methane.
The shortage of natural gas, which is predominantly methane, has greatly increased the need for economic production of synthetic natural gas. Gasification of carbonaceous materials, for example coal, produces a low BTU gas generally having a fuel value below 300 BTU per standard cubic foot, which is too low for most natural gas uses. Methane has a heat of combustion of 1013 BTU/ft.sup.3. A large number of processes have been proposed for enhancing the heat value of low BTU gases. Many of these processes produce what is called an intermediate BTU gas.
The low BTU gases are hydrogen deficient for methane production. Moreover, the heating value is low if the nitrogen is not removed. The economics is also affected by the number of reactions, and gas treating and separation steps required to produce a high methane content gas. This is affected by the purity of the various reaction streams and final product.
Accordingly, it is an object of this invention to provide a method of producing a high BTU product in a way that effectively uses the carbon monoxide and hydrogen in the feed gas, that separates nitrogen during hydrogen production, that tends to produce a single methane product, that produces a final product that requires no further treatment except water removal, and that uses less energy to separate and produce hydrogen from the producer gas.